Triphasic process for gas effluent treatment

ABSTRACT

A triphasic bioreactor for physico-chemically treating a gas is disclosed. The triphasic bioreactor comprises a reaction chamber with a liquid and biocatalysts in suspension in the liquid, for catalyzing a reaction between the gas and the liquid to obtain a treated gas and a solution containing a reaction product. A gas bubbling means is provided in the reaction chamber for bubbling the gas to be treated into the liquid thereby dissolving the gas into the liquid and increasing a pressure inside the reaction chamber. The bioreactor further comprises a liquid inlet in fluid communication with the reaction chamber for receiving the liquid and filling the reaction chamber, a liquid outlet in fluid communication with the reaction chamber for releasing the solution and a gas outlet in fluid communication with the reaction chamber to release the treated gas. The bioreactor further comprises a retention device to retain the biocatalysts in the reaction chamber. The invention also concerns a process using the triphasic bioreactor. The triphasic bioreactor may advantageously be used for removing carbonic dioxide from a CO 2 -containing gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 10/195,848 filed Jul.12, 2002 now U.S. Pat. No. 7,176,017. This application also claimspriority from Canadian application No. 2,353,307 filed Jul. 13, 2001.The aforementioned applications are incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

This invention relates to the field of gas effluent treatment and airpurification. More specifically, it concerns a triphasic bioreactor forthe biological treatment of gaseous effluent. The invention alsoconcerns a triphasic process for the biological treatment of gaseffluent.

BACKGROUND

Contemporary industrial activities generate gaseous effluents containinga multitude of chemical compounds and contaminants which interfere withthe equilibrium of elements in nature and affect the environment atdifferent levels. Acid rain, the green-house effect, smog and thedeterioration of the ozone layer are examples that speak volumes aboutthis problem. Reduction of noxious emissions is therefore notsurprisingly the subject of more and more legislation and regulation.Industrial activities and applications which must contend with stricterenvironmental regulatory standards in order to expect any long termcommercial viability, will turn more and more to biological andenvironmentally safe methods. Consequently, there is a real need for newapparatus and methods aimed at the biological treatment of gaseous wasteor effluents.

There already exists a vast array of technologies aimed at theseparation and recovery of individual or mixed gases and a number ofdifferent biological methods is known to treat gaseous waste oreffluents: bacterial degradation (JP 2000-287679; JP2000-236870),fermentation by anaerobic bacteria (WO 98/00558), photosynthesis througheither plants (CA 2,029,101 A1; JP04-190782) or microorganisms (JP03-216180). Among the more popular are those gained through theharnessing of biological processes such as peat biofilters sprinkledwith a flora of microorganisms in an aqueous phase, or biofilter columnscomprising immobilized resident microorganisms (Deshusses et al. (1996)Biotechnol. Bioeng. 49, 587-598). Although such biofilters havecontributed to technological advances within the field of gaseous wastebiopurification, the main drawbacks associated with their use are theirdifficult maintenance and upkeep, lack of versatility, as well as timeconsuming bacterial acclimation and response to perturbation periods(Deshusses et al.).

A number of biological sanitation/purification methods and products isknown to use enzymatic processes, coupled or not to filtration membranes(S5250305; U.S. Pat. No. 4,033,822; JP63-129987). However, these areneither intended nor adequate for the cleansing of gaseous waste oreffluents. The main reason for this is that, in such systems,contaminants are generally already in solution (U.S. Pat. No. 5,130,237;U.S. Pat. No. 4,033,822; U.S. Pat. No. 4,758,417; U.S. Pat. No.5,250,305; WO97/19196; JP63-129987). Efficient enzymatic conversion andtreatability itself of gaseous waste or effluents in liquids thereforedepend on adequate and sufficient dissolution of the gaseous phase inthe liquid phase. However, the adequate dissolution of gaseous waste oreffluents into liquids for enzymatic conversion poses a real problemwhich constitutes the first of a series of important limitations whichcompound the problem of further technological advances in the field ofgas biopurification.

Although triphasic <<Gas-Liquid-Solid>> (GLS) reactors are commonly usedin a large variety of industrial applications, their utilization remainsquite limited in the area of biochemical gas treatment (U.S. Pat. No.6,245,304; U.S. Pat. No. 4,743,545). Also known in the prior art are theGLS bioprocesses abundantly reported in the literature. A majority ofthese concerns wastewater treatment (JP09057289). These GLS processesare characterized in that the gaseous intake serves the sole purpose ofsatisfying the specific metabolic requirements of the particularorganism selected for the wastewater treatment process. Such GLStreatment processes are therefore not aimed at reducing gaseousemissions.

As previously mentioned, these systems are neither intended nor adequatefor the treatment of gaseous waste or effluents. An additional problemassociated with the use of these systems is the non retention of thesolid phase within the reactor. Biocatalysts are in fact washed rightout of the reactors along with the liquid phase. Different concepts are,nonetheless, based on this principle for the reduction of gaseousemissions, namely carbon dioxide. Certain bioreactors allow the uptakeof CO₂ by photosynthetic organisms (CA229101; JP03-216180) and similarprocesses bind CO₂ through algae (CA2232707; JP08-116965; JP04-190782;JP04-075537). However, the biocatalyst retention problem remains largelyunaddressed and constitutes another serious limitation, along withgaseous effluent dissolution, to further technological advancements.

The main argument against the use of ultrafiltration membranes to solvethis biocatalyst retention problem is their propensity to clogging.Clogging renders them unattractive and so their use is rather limitedfor the retention of catalysts within reactors. However, aphotobioreactor for medical applications as an artificial lung(WO9200380; U.S. Pat. No. 5,614,378) and an oxygen recovery system (U.S.Pat. No. 4,602,987; U.S. Pat. No. 4,761,209) are notable exceptionsmaking use of carbonic anhydrase and an ultrafiltration unit.

The patent applications held by the assignee, CO2 Solution Inc., via LesSystémes Envirobio Inc. (EP0991462; WO9855210; CA2291785) proposes apacked column for the treatment of carbon dioxide using immobilizedcarbonic anhydrase without the use of an ultrafiltration membrane.Carbonic anhydrase is a readily available and highly reactive enzymethat is used in other systems for the reduction of carbon dioxideemissions (U.S. Pat. No. 4,602,987; U.S. Pat. No. 4,743,545; U.S. Pat.No. 5,614,378; U.S. Pat. No. 6,257,335). In the system described byTrachtenberg for the carbonic anhydrase treatment of gaseous effluents(U.S. Pat. No. 6,143,556; CA2222030), biocatalyst retention occursthrough a porous wall or through enzyme immobilization. However,important drawbacks are associated with the use of enzymeimmobilization, as will be discussed below.

Other major drawbacks are associated with the use of enzymatic systems.One of these stems from systems where enzymatic activity is specificallyand locally concentrated. This is the case with systems where enzymesare immobilized at a particular site or on a specific part of anapparatus. Examples in point of such systems are those where enzymes areimmobilized on a filtration membrane (JP60014900008A2; U.S. Pat. No.4,033,822; U.S. Pat. No. 5,130,237; U.S. Pat. No. 5,250,305;JP54-132291; JP63-129987; JP02-109986; DE3937892) or even, at agas-liquid phase boundary (WO96/40414; U.S. Pat. No. 6,143,556). Thelimited surface contact area obtainable between the dissolved gassubstrate, the liquid and the enzyme's active site poses an importantproblem. Hence, these systems generate significantly greater waste ofinput material, such as expensive purified enzymes, because the contactsurface with the gaseous phase is far from optimal and limits productivereaction rates. Therefore, as mentioned previously, overcoming thecontact surface area difficulty should yield further technologicaladvances.

Other examples of prior art apparatuses or methods for the treatment ofgas or liquid effluent are given in the following documents: CA2160311;CA2238323; CA2259492; CA2268641; JP2000-236870; JP2000-287679;JP2000-202239; U.S. Pat. No. 4,758,417; U.S. Pat. No. 5,593,886; U.S.Pat. No. 5,807,722; U.S. Pat. No. 6,136,577; and U.S. Pat. No.6,245,304.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an apparatus that isdistinct from and overcomes several disadvantages of the prior artbioreactor for the treatment of gas effluent, as will be discussed indetail below.

In accordance with the present invention, that object is achieved with atriphasic bioreactor for physico-chemically treating a gas effluent. Thetriphasic bioreactor comprises a reaction chamber, a liquid inlet andgas and liquid outlets in fluid communication with the reaction chamber.A gas bubbling means is also provided within the reaction chamber forreceiving the gas to be treated. The reaction chamber is filled withbiocatalysts in suspension in a liquid, for catalyzing a reactionbetween the gas and the liquid to obtain a treated gas and a solutioncontaining a reaction product. The liquid is preferably an aqueous ororganic solution of an appropriate composition with respect to thedesired catalytic reaction. The liquid inlet is for receiving the liquidinto the reaction chamber and filling it. The gas bubbling means is alsofor bubbling the gas to be treated into the liquid thereby bothdissolving it into the liquid and increasing the gas pressure inside thereaction chamber. The bioreactor further comprises a retention devicefor retaining the biocatalysts within the reaction chamber while theliquid outlet allows for the pressure release of the solution containingthe reaction product.

The triphasic bioreactor of the present invention provides theadvantages of biologically treating gaseous waste and effluents whilesimultaneously providing biocatalysts in liquid suspension, optimizinggas phase dissolution into the liquid phase and thereby optimizingsurface contact area between the gas, liquid and solid phases, as wellas retaining the biocatalysts within the reactor while allowing thepressure release of liquid containing a reaction product exempt ofbiocatalysts.

In accordance with a preferred aspect of the invention, the bioreactorcomprises a pressure regulating valve to control a pressure created bythe gas bubbled within the reaction chamber and a sampling means forsampling and analyzing liquid from the reaction chamber.

The gas bubbling means preferably comprises a gas inlet of the reactionchamber to receive the gas to be treated and a bubbler located in abottom portion of the reaction chamber. The bubbler has a gas inletconnected to the gas inlet of the reaction chamber and a plurality ofgas outlets to diffuse the gas in the reaction chamber. The gas bubblingmeans further comprises a pipe to connect the gas inlet of the reactionchamber to the gas inlet of the bubbler.

The biocatalysts used in the bioreactor are preferably selected from thegroup consisting of enzymes, liposomes, microoganisms, animal cells,plant cells and a combination thereof. Most preferably, the biocatalystsare entrapped in porous substrates pervading the reaction chamber.Alternatively, the biocatalysts may be carried by the liquid that feedsthe reaction chamber.

The retention device preferably comprises a filter having pores with asmaller diameter than the diameter of the biocatalysts. More preferably,the filter is a membrane filter.

In accordance with a first preferred embodiment, the membrane filter islocated inside the reaction chamber upstream from the liquid outlet.

In accordance with a second preferred embodiment, the membrane filter islocated outside the reaction chamber. In such a case, the retentiondevice further comprises a first piping means and a second piping means.The first piping means is for piping liquid, which contains biocatalystsand reaction products, from the liquid outlet of the reaction chamber tothe membrane filter where a permeate liquid containing the reactionproducts is separated from a retentate liquid containing thebiocatalysts. The second piping means is for piping the retentate liquidto the liquid inlet of the bioreactor.

In accordance with a preferred aspect of the invention, the triphasicbioreactor is used for reducing carbon dioxide contained in a gaseffluent. In such a case, the gas effluent to be treated contains carbondioxide, the liquid filling the bioreactor is an aqueous liquid and thebiocatalysts are enzymes capable of catalyzing the chemical conversionof the dissolved carbon dioxide into an aqueous solution containinghydrogen ions and bicarbonate ions. More preferably, the enzymes arecarbonic anhydrase.

In accordance with a still further preferred aspect of the invention,the bioreactor comprises an additional reaction chamber, as definedhereinabove, in series with the reaction chamber, hereinafter referredto as the first reaction chamber, to further treat the previouslytreated gas. In such a case, the biocatalysts filling the first reactionchamber are preferably different from the biocatalysts filling theadditional reaction chamber.

The present invention also provides a method for the biocatalytictreatment of gas effluent which is basically a three-step process.

First, a reaction chamber filled with biocatalysts is filled with aliquid thereby suspending the biocatalysts in the liquid. Second, a gasto be treated is bubbled into the liquid thereby dissolving it into theliquid and creating a pressure inside the reaction chamber. The bubblingthereby promotes the biocatalytic reaction between the liquid and thegas to be treated in order to obtain a treated gas and a solutioncontaining a reaction product. Third, the solution containing thereaction product is released by pressure from the reaction chamberwhilst retaining the biocatalysts within the reaction chamber. Duringthe second and third steps, the pressure is controlled within thereaction chamber and treated gas is released from the reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the detailed description and upon referring to the drawings inwhich:

FIG. 1 is a cross-sectional side view of a triphasic bioreactoraccording to a first preferred embodiment of the invention.

FIG. 2 is a schematic side view of a triphasic bioreactor according to asecond preferred embodiment of the invention having an externaltangential flow filter.

FIG. 3 is a schematic side view of a triphasic bioreactor according toanother embodiment of the invention, having an integrated filter.

FIG. 4 is a schematic side view of a triphasic bioreactor according to afurther embodiment, having an integrated tangential flow filter.

FIG. 5 is a schematic side view of a triphasic bioreactor according to astill further embodiment, having a filter cartridge.

FIG. 6 is a schematic side view of a series of linked triphasicbioreactors for the treatment of gas effluent.

While the invention will be described in conjunction with exampleembodiments, it will be understood that it is not intended to limit thescope of the invention to such embodiments. On the contrary, it isintended to cover all alternatives, modifications and equivalents as maybe included as defined by the appended claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring to FIG. 1 or 2, the triphasic bioreactor (1) is an apparatusfor physico-chemically treating a gas (10). Minimally, it features areaction chamber (2) filled with biocatalysts (4) in suspension in aliquid (3), a liquid inlet (5) and liquid (6) and gas (7) outlets influid communication with the reaction chamber (2). It is worth notingthat the use of the article “a” means “at least one” and hence atriphasic bioreactor according to the invention may advantageouslycomprise more than one reaction chamber, and/or more than one liquid andgas outlet and inlets. The liquid inlet (5) is for receiving the liquid(3) and filling the reaction chamber (2). The reaction chamber (2) ismade of an appropriate material that could be glass, plastic, stainlesssteel, a synthetic polymer or other suitable material.

A gas bubbling means (8) and a retention device (9) are also provided.The gas bubbling means (8) is for receiving the gas (10), or gases, tobe treated inside the reaction chamber (2) and for bubbling it into theliquid (3) thereby both dissolving the gas to be treated (10) into theliquid (3) and creating a pressure within the reaction chamber (2). Thebiocatalysts (4) are chosen so as to be able to biocatalyze a reactionbetween the gas (10) to be treated and the liquid (3) in order to obtaina treated gas (11) and a solution (12) containing a reaction product.The liquid outlet (6) is for releasing by pressure the solution (12)containing the reaction product while the retention device (9) retainsthe biocatalysts (4) within the reaction chamber (2). The gas outlet (7)is for releasing the treated gas (11) from the reaction chamber (2).

The triphasic bioreactor (1) preferably includes a pressure regulatingvalve (13) to control the pressure created by the gas (10) bubbled intothe reaction chamber (2). The pressure regulating valve (13) may belocated in the gas outlet (7). The triphasic bioreactor (1) may alsoinclude a valve (14) at the liquid outlet (6) and/or at the liquid inlet(5) for regulating the flow of liquid (3) into and out of the reactionchamber (2). As will become more apparent further along in thedescription, these features are used for both regulating the pressureinside the reaction chamber (2) so as not to exceed the pressure limitsthe apparatus may withstand, but also to better control the pressurerelease of the solution (12) containing the reaction product.

As shown in FIG. 2, the triphasic bioreactor (1) may include a mixer(15) within the reaction chamber (2) to mix the liquid (3), thebiocatalysts (4) and the gas (10). Any type of mixer known in the artcould be used. For example, as shown in FIG. 2, the mixer (15) mightinclude an axial propeller (16) operatively connected to a top cover(18) of the reaction chamber (2) by means of a driving shaft (17). Insuch a case, the bioreactor also comprises a suitable driving means fordriving the shaft into rotation.

In order to drive forward the reaction between the gas to be treated(10) and the liquid (3), the biocatalysts (4) must comprise a moleculecapable of reacting with the substrates, namely the dissolved gas (10)and the liquid (3), so as to yield a treated gas (11) and a solution(12) containing a reaction product. Biocatalysts comprising such amolecule may be selected from a wide variety of biological materialsincluding enzymes, liposomes, microoganisms, animal cells and/or plantcells and the like. Fractions, complexes or combinations thereof mayalso be used simultaneously. Fractions of enzymes may comprise, forexample, specific sub-units of an enzyme, such as its catalyticsub-units. Fractions of a microorganism, animal or plant cell maycomprise, for example, specific sub-cellular organelles or compartmentssuch as cellular membranes, ribosomes, mitochondria, chloroplasts orfractions such as cytoplasmic or nuclear extracts. For the purpose ofthe invention, the biocatalysts may also be entrapped in a poroussubstrate, for example, an insoluble gel particle such as silica,alginate, alginate/chitosane, alginate/carboxymethylcellulose, etc. Forthe purpose of the invention, biocatalysts may also be immobilized onsolid packing in suspension in the liquid, such as enzymes covalentlybound to plastic packing. Alternatively, enzymes might be in a freestate, or chemically linked in an albumin or PEG network. All of thesebiological materials, which may be obtained through routine methods thatare well documented in the scientific literature and known to the personskilled in the art, may be made of use with the present invention whichis quite versatile.

Retention of the biocatalysts (4) inside the reaction chamber (2) is animportant feature of the invention as biological materials are oftenquite expensive. In order to allow the pressure release of solution (12)containing the reaction product whilst retaining the biocatalysts (4)within the reaction chamber (2), the retention device (9) must beadapted according to the relative and respective sizes of the reactionproducts and the biocatalysts (4), as well as co-factors whenappropriate.

Pressure release of the solution (11) containing the reaction productmay be likened to pressure filtration such as ultrafiltration ormicrofiltration, which are defined as the action of filtering a solutionthrough a fine membrane by pressure. “Ultrafiltration” is a term whichis, in the strict sense, reserved for the physical separation ofparticles of 0.005 to 0.1 μm in size.

Although, in a variety of its embodiments the present invention may makeuse of ultrafiltration or microfiltration membranes (19) (20), as shownin FIGS. 2-6, it is by no means restricted to their use. For instance,depending upon the size of the biocatalysts and reaction product, anappropriate retention device (9) may comprise a simple grid and/orperforated base, at the bottom of the reaction chamber (2), as shown inFIG. 1, for slowing the flow of solution (11) containing the reactionproduct from the reaction chamber (2) whilst retaining the biocatalysts(4) inside the reaction chamber (2).

In the present invention, pressure is generated within the reactionchamber (2) by bubbling the gas to be treated (10) into the liquid (3).This pressure contributes to the dissolution of the gas to be treated(10) inside the liquid (3) containing the biocatalysts (4) and thereforeto its further physico-chemical transformation. The partial pressureinside the reaction chamber (2) is greater on one side of the retentiondevice (9). There is consequently greater dissolution of gas to betreated according to the law of dissolution of gases, known as the lawof Henry, which states that the concentration of a given dissolved gasis proportional to its partial pressure in the atmosphere at the surfaceof the liquid. As stated above, the retention device (9) preferablycomprises a filter (19). If the biocatalyst materials are sub-micronsparticles, for example in the range of 0.005 to 0.1 μm in size, amembrane filter is preferably used. Such a membrane filter may be madeof cellulose, nylon, polymethyl methacrylate, PVDF or the like, withpores having a smaller diameter than the diameter of the biocatalysts,and co-factors when appropriate.

As shown in FIGS. 1, and 3 to 5, the membrane filter (19) may beintegrated inside the reaction chamber (2) upstream from the liquidoutlet (6). In such an embodiment, the liquid flows perpendicularly tothe filter (19) as in classic frontal filtration. Appropriate pore sizeallows permeate liquid (12) to exit through the filter (19) exempt ofbiocatalysts (4). The solution (12) containing the reaction product musttherefore pass through the filter (19) first in order to be able to exitthe reaction chamber (2) via the liquid outlet (6). The permeate liquid(12) or filtrate released may then be discarded or conveyed/piped toother treatment units for further treatment such as decantation, ionexchange, etc.

Alternatively, the bioreactor (1) may include an integrated filtercartridge (20) fixed inside the reaction chamber (2) and positioned atthe desired height within the reaction chamber (2), as shown in FIG. 5.The filter cartridge (20) is linked directly to the non-pressurizedliquid outlet (6) and allows for filtration of the solution (11)containing the reaction product, but not the biocatalysts (4), directlyinto the liquid outlet (6). As mentioned above, the pore size of themembrane (19) inside the cartridge (20) is dependent upon both the sizeof the biocatalysts (4) and the reaction product, as well as co-factorswhen appropriate.

Optionally, the bioreactor (1) may also incorporate a closed loopcircuit (21) including a pump (22) to circulate liquid tangentially tothe membrane (19), as shown in FIGS. 2 and 4. This particular embodimentof the invention is different because instead of being perpendicular tothe filter, the flow of liquid is “tangential” relatively to the filtermembrane (19). Liquid therefore “sweeps” the filter membrane (19)tangentially thereby promoting recirculation of the liquid (3) and thebiocatalysts (4). The captive biocatalysts (4) therefore remain inliquid suspension. Clogging of the pores of the membrane filter isconsequently considerably reduced.

In accordance with a second preferred embodiment of the invention, themembrane filter (19) may be located outside of the reaction chamber (2),as shown in FIGS. 2 and 6. According to this particular embodiment, theretention device (9) will further include a first pipe (22), or anyother means adapted to convey a liquid, for piping the solution (12)containing biocatalysts (4) and reaction products from the liquid outlet(6) of the reaction chamber (2) to the membrane filter (19) where apermeate liquid (12) e.g. the solution (12) containing the reactionproducts, is separated from the retentate liquid (26) containing thebiocatalysts (4). In such an embodiment, the retention device (9)further comprises a second pipe for piping the retentate liquid (26)back to the liquid inlet (5) and into the bioreactor's reaction chamber(2). The permeate liquid (12) may be discarded, or conveyed/piped toother treatment units for further treatment such as decantation, ionexchange etc.

An important feature of the invention is the gas bubbling means (8). Inone embodiment of the triphasic bioreactor, the gas bubbling means (8)preferably comprises a bubbler (24) or a number of these, as shown inFIG. 1, located in the bottom portion of the reaction chamber (2). Thebubbler (24) has a gas inlet (29) connected to a gas inlet (23) of thereaction chamber (2) by means of a suitable pipe (27), to receive thegas effluent (10) to be treated. The bubbler (24) also comprises aplurality of gas outlets (28) to diffuse the gas in the reaction chamber(2).

As shown in FIG. 1, the gas bubbling means may include a bubbler (24) inthe form of a removable cap, made of a foam-like material, covering agas outlet nozzle, at the bottom portion of the triphasic bioreactor(2). Foam-like material is advantageous as it provides the plurality ofgas outlets (28) needed to diffuse very fine bubbles and contributes totheir uniform distribution within the liquid (3) containing thebiocatalysts (4). The reduction in size of the gas bubbles enhances bothgas dissolution and contact surface between gas (10) and liquid (3)phase reactants and the biocatalysts (4). As stated above, the inventionmay include a mixer (15) in order to enhance the uniform distribution ofgas (10) bubbles and biocatalysts (4) within the liquid (3).

The relative size and dimensions of the reaction chamber (2), as well asthe relative porosity of the filter membranes used, if any, is dependentupon particular usage requirements and directly proportional to theliquid flow rates required. As expected, liquid flow rates may varygreatly between different applications. Appropriate dimensionadjustments and allowances should therefore be made when passing fromone type of application to the other.

In accordance with a preferred aspect of the invention, the triphasicbioreactor is used for removing carbon dioxide from a gas effluent (10)containing carbon dioxide. In such a case, the liquid (3) filling thereaction chamber (2) is an aqueous solution, preferably water, and thebiocatalysts (4) are enzymes capable of catalyzing the chemicalconversion of the dissolved carbon dioxide into an aqueous solution (12)containing hydrogen ions and bicarbonate ions. The enzymes are,preferably, carbonic anhydrase.

The transformation of CO₂ into bicarbonate ions, usually a slownaturally occurring process, is catalyzed by the enzyme in suspension inthe reaction chamber (2). Without catalysis, the equilibrium reactionmust undergo an intermediate hydration that slows the transformation ofCO₂ into bicarbonate ions. The following equations describe the relevantprocesses:without enzyme: dissolved CO₂→H₂CO₃→H⁺+HCO₃ ⁻  (I)with enzyme: dissolved CO₂→H⁺+HCO₃ ⁻  (II)

The enzyme carbonic anhydrase, which is of relatively low molecularweight (30,000 daltons), may be made to form part of a complex in orderto increase its size. This, in turn, allows the use of membranes withgreater porosity and enhances liquid flow rates. Different types ofenzyme complexes may be formed. Among these are those using whole cellssuch as red blood cells. However, with red blood cells, the enzymesrapidly leak out and are lost. Encapsulation techniques may thereforeovercome this problem. Enzymes may be immobilized on solid packing.Packing made of polymers such as nylon, polystyrene, polyurethane,polymethyl methacrylate, functionalities silica gel, etc. may be used.Enzymes may also be entrapped in insoluble gel particles such as silica,alginate, alginate/chitosane or alginate/carboxymethylcellulose, etc. orcovalently linked or non covalently linked in a network of albumin, PEGor other molecule. Such a network constitutes a loose type network. Itmay appear as a cloudy suspension, “filaments” of which are oftenvisible to the naked eye. For the purpose of the invention, alginateparticles should preferably possess a diameter comprised in a range from1 to 9 mm, and preferably, a diameter inferior to 3 mm.

Thanks to the different features of the triphasic bioreactor, such asthe bubbling means and the enclosed reactor filled with the aqueousliquid, the pressure obtained inside the reaction chamber (2) permitsthe gas effluent containing carbon dioxide to rapidly dissolve into theliquid (3) which contains the carbonic anhydrase biocatalysts (4),thereby optimizing the reaction conditions of reaction (II). Atangential flow filtration system, such as shown in FIGS. 2, 4 and 6,allows the solution (12) containing the bicarbonate ions to be releasedfrom the reaction chamber (2) while part of the liquid containing thecarbonic anhydrase biocatalysts (4) is returned to the reaction chamber(2).

In order to better monitoring the parameters of the reaction processsuch as pH, temperature, reaction by-product concentration, etc., thetriphasic bioreactor (1) may incorporate a sampling means (25) forsampling and analyzing liquid from inside the reaction chamber, as shownin FIG. 2. As well, thermoregulation circuits may be added onto thereaction chamber in order to optimize temperature conditions. Gascomposition analyzers may also be provided at the gas inlet (5) and/oroutlet (7). Additional valves may also be added onto the liquid and gasinlets and outlets in order to better regulate the flow rates of thedifferent phases, the level of liquid inside the reaction chamber, thepressure inside the reaction chamber, etc.

In yet another embodiment, the invention may consist in a series ofreaction chambers (2), with one or more additional reaction chambers, asshown in FIG. 6. These may be linked so as to treat gas simultaneouslyor sequentially. In reaction chambers linked in succession, as shown inFIG. 6, the gas outlet (7) which releases the treated gas from onereaction chamber (2) may be linked in fluid communication to the nextreaction chamber (2) through its gas inlet (23). This allows for furtheror extensive treatment of the gas. The number of reaction chamberstherefore depends on the extent of gas treatment required. Extensive orfurther treatment might entail treating the gas repeatedly in successivereaction chambers, all of which contain the same biocatalysts. However,extensive or further treatment might also entail different treatments insuccession, the particular biocatalysts varying from one reactionchamber to the next. Therefore biocatalysts in one reaction chamber maybe different from the biocatalysts in the other reaction chamber(s) insuch a series.

Another object of the invention is to provide a triphasic process forphysico-chemically treating a gas effluent. The process of the inventionis basically a three-step process. First, a reaction chamber, filledwith the biocatalysts (4) in suspension in the liquid (3), is provided.Second, the gas to be treated (10) is bubbled into the liquid (3) in thereaction chamber (2) in order to dissolve the gas to be treated (10)into the liquid (3) and to increase a pressure within the reactionchamber (2). Bubbling thereby promotes the biocatalytic reaction betweenthe liquid (3) and the gas (10) in order to obtain a treated gas (11)and a solution (12) containing a reaction product. Third, the solution(12) containing a reaction product is pressure released from thereaction chamber (2) whilst retaining the biocatalysts (4) within thereaction chamber (2). All the while during the second and third steps,the pressure is controlled within the reaction chamber (2) and a treatedgas (11) is released from the reaction chamber (2).

In yet another embodiment of the invention, the last step of the processmay occur through ultrafiltration. The ultrafiltration may be conductedeither inside or outside of the reaction chamber.

Although preferred embodiments of the present invention have beendescribed in detail herein and illustrated in the accompanying drawings,it is to be understood that the invention is not limited to theseprecise embodiments and that various changes and modifications may beeffected therein without departing from the scope or spirit of thepresent invention.

1. A triphasic process for physico-chemically treating a gas containingcarbon dioxide, comprising the steps of: a) providing a reaction chamberwith a liquid and biocatalysts, the biocatalysts comprising carbonicanhydrase and being suspended in the liquid; b) bubbling the gas to betreated into the reaction chamber to dissolve the gas into the liquidand to increase a pressure within the reaction chamber, therebypromoting the chemical conversion of the dissolved carbon dioxide intoan aqueous solution containing hydrogen ions and bicarbonate ions,hereinafter referred to as the reaction products, and obtaining atreated gas; c) releasing the solution obtained in step b) from thereaction chamber whilst retaining the biocatalysts within the reactionchamber; and d) during steps b) and c) controlling the pressure withinthe reaction chamber and releasing the treated gas obtained in step b).2. A process according to claim 1, wherein step c) of retainingcomprises an ultrafiltration of the solution obtained in step b).
 3. Aprocess according to claim 2, wherein the ultrafiltration is conductedinside or outside the reaction chamber.
 4. A process according to claim1, wherein in step c), the solution obtained in step b) is released bypressure.
 5. A process according to claim 1, wherein the biocatalystsconsisting of carbonic anhydrase suspended in the liquid are provided ina free state, linked to a solid support or entrapped in an organic orinorganic solid substrate.
 6. The process according to claim 1, whereinthe biocatalysts comprising carbonic anhydrase are provided on solidsupports, the solid supports being suspended in the liquid.
 7. Theprocess according to claim 1, wherein the biocatalysts comprisingcarbonic anhydrase are entrapped in an organic or inorganic solidsubstrate, the organic or inorganic solid substrate being suspended inthe liquid.
 8. The process of claim 7, wherein the biocatalystscomprising carbonic anhydrase are entrapped in a porous substrate whichis suspended in the liquid.
 9. The process of claim 8, wherein theporous substrate comprises particles composed of an insoluble gel,silica, alginate, alginate/chitosan, or alginate/carboxymethylcellulose,or a combination thereof.
 10. The process of claim 1, wherein thebiocatalysts comprising carbonic anhydrase are immobilized on a solidpacking, said solid packing being suspended in the liquid.
 11. Theprocess of claim 1, wherein the biocatalysts comprising carbonicanhydrase are chemically linked in an albumin or PEG network.
 12. Theprocess according to claim 1, wherein the biocatalysts comprisingcarbonic anhydrase are provided in a free state suspended in the liquid.13. The process according to claim 1, wherein the biocatalysts consistof carbonic anhydrase.
 14. The process according to claim 13, whereinthe biocatalysts consisting of carbonic anhydrase are provided on solidsupports suspended in the liquid, are provided entrapped in an organicor inorganic solid substrate suspended in the liquid, are providedimmobilized on a solid packing in suspension in the liquid, arechemically linked in an albumin or PEG network, or are provided in afree state suspended in the liquid.
 15. The process according to claim1, wherein step c) of retaining comprises filtration.
 16. The processaccording to claim 1, wherein step c) of retaining comprises providing agrid or a perforated base at a bottom part of the reaction chamber. 17.The process according to claim 1, wherein a filter membrane allowsretaining of step c), and further comprises circulating the liquidtangentially with respect to the filter membrane.
 18. The processaccording to claim 1, wherein the retaining of step c) is performed by aretention device and wherein step d) of controlling the pressure withinthe reaction chamber comprises maintaining a partial pressure of the gasinside the reaction chamber greater than the partial pressure on theother side of the retention device.